The invention relates to a process for the seam welding of sheet metal blanks of unequal thickness. In so-called sheet metal welding, in particular, in which two or more sheet metal blanks or panels are joined together into larger panel configurations, it is necessary to an increasing extent also to weld together sheet metals of varying thickness and surface quality. The welding processes used--mash seam welding and laser welding--encounter specific difficulties, however, in this connection.
With mash seam welding (a particular form of electric resistance roll seam welding between two electrode rollers), the zone with the highest temperature is more or less symmetrically set between the contact surfaces of the electrodes; in the case of sheet metals of sharply varying thickness, this zone consequently occurs mainly within the cross-section of the thicker metal sheet, and therefore is offset in relation to the jointing plane between the metal sheet edges which overlap each other. In order to obtain nevertheless a reliable welding of both edges, increased electrical power is necessary, and welding can occur only at considerably reduced speed (compared with the welding of metal sheets of equal thickness). The asymmetrical position of the zone with the highest temperature may also have the result that more or less deep and inadequately welded gaps remain, running from the edges of the metal sheets, which are undesirable with regard to corrosion and mechanical strength (fluctuating loading and workability). Finally, the thickening and/or the thickness transition along the mash seam are relatively large, which once again can cause problems, e.g. during subsequent deep-drawing of the welded workpieces.
An "asymmetry" of a different kind occurs during laser welding with metal sheet edges butted together. Whilst with metal sheets of equal thickness the laser beam is exactly perpendicular to the metal sheet plane and aligned with the butt joint, it has to be set slightly obliquely to a joint, with unequally "high" edges. However, the depth effect of the beam in the joint (parallel to the edge abutment) is drastically reduced thereby, and the fusing of the two metal sheet edges occurs with considerable asymmetry. Even with the laser process, sheet metal blanks of different thicknesses can for this reason only be welded at a considerably reduced rate of feed and with the risk of reduced seam quality.
The difficulties mentioned, which occur in the seam welding of sheet metal blanks of unequal thickness without additional material, are intended to be overcome with the invention. In particular, the rate of feed is intended to approximate to that in the seam welding of metal sheets of equal thickness, and the quality of the welding seam is intended to be better controlled, i.e. to be more reliably produced.